A textured semiconductor surface reduces reflection across wide bands of incident light thereby increasing absorbed light intensity. Such semiconductors may be used in the manufacture of solar cells. Solar cells are devices that convert light energy incident on their surfaces such as sunlight into electric energy. Reducing the reflectance of light incident on the surface improves conversion efficiency into electric energy. Texturing, however, is not restricted to semiconductors in the manufacture of solar cells but also may be used in the manufacture of photovoltaic devices in general, optical and electrochemical detectors/sensors, biodetectors/biosensors, catalysts, electrodes, and other devices where reducing the reflectance of incident light improves the efficiency of the device.
Known techniques for wet chemical pyramidal (tetragonal) structure texturing of (100)-orientated silicon surfaces use alkaline media, such as solutions of alkali hydroxides, alkali carbonates, ammonia or choline. Alkali hydroxides by themselves produce unevenly textured surfaces which result in areas of high reflectivity. An additive is typically included to control the texturing rate and to form repeatable pyramid structures. Solutions of hydrazine or ethylene diamine or pyrocatechol can be used instead of alkali hydroxides but they are disadvantageous on account of their toxicity to workers. The most common formulations include water, sodium or potassium hydroxide and alcohol. The alcohol component may be used to control the etch rate of the alkali hydroxides. The alcohol component used is either ethylene glycol or isopropanol. Although isopropanol is included in many conventional texturing compositions, its low boiling point and low flash point are undesirable properties for texturing compositions.
WO 2011/052941 discloses examples of alkaline etching compositions which exclude isopropanol for texturing crystalline silicon based wafers to form pyramid structures. The etching compositions include at least one alkaline compound, at least one cyclic compound having a boiling point of 100-400° C. and the balance of the formulation is water. The cyclic compounds are included to inhibit over etching of the silicon by the alkaline compounds. The cyclic compounds are C4-C10 heterocyclic compounds with one or more heterogeneous elements selected from nitrogen, oxygen and sulfur. The cyclic compounds are included in amounts of 0.1-50 wt % of the etching composition. Although there are alkaline texturing compositions which exclude isopropanol for the formation of pyramid structures on crystalline silicon wafers, there is still a need for an improved alkaline texturing composition and method for forming pyramid structures on crystalline silicon wafers.